The present invention relates to a process for the catalytic decomposition of chlorofluoro-alkanes commonly named as "flons". More particularly this invention relates to a process for decomposing chlorofluoro-alkanes to non hazard compounds by using the catalysts in the presence of steam.
Chlorofluoro-alkanes, wherein the hydrogens of hydrocarbon are wholly or partially substituted with fluorines and chlorines (hereinafter may be abbreviated as flons) are stable both in chemical and thermal properties, non-toxic and has no smell. For that reason, have been widely used as the most safe substances for refrigerant, foaming agent, solvent and so on.
However, recently among these flons, particularly chlorofluorocarbons(CFC), wherein all of the hydrogen atoms are substituted with fluorines and chlorines, have been found to be decomposed in the ozon layer of the stratosphere and to have high possibility of destructing the ozon layer. It has been determined that the production of such flons should be gradually reduced by substituting the one which does not destruct the ozon layer for them.
Accordingly, in aaddition to the development of such substitute, the development of the process of decomposing the presently used flons into the substances which are no fear of destructing the ozone layer before giving off the flons into air has been desired.
However, such flons are extremely stable compounds, poor in the reactivity and are considered to be difficult to act on the decomposition reaction. Plasma method of decomposition at very high temperature and so on are known.
On the other hand, the process of the decomposition comprising in contacting the flons in addition to steam and air with zeolite catalyst at 400.degree. to 700.degree. C. has recently reported, but presently only a few of the reports concerning the study of catalytic decomposition reaction have been published.
However, as a method of treating the exhausted gases such a large scaled and high cost method as plasma method is difficult in applications, so it is almost impossible to really use it for the solution of ozon-problem. In order to be easily applicable by users of flons in the place where they are used, and prevent environmental pollution from occurring, the preferable method is simply to decompose flons by means of catalyst. Accordingly, the object of this invention is to provide the simple decomposing method by contacting flons with catalyst into harmless substances without hazard of destructing the ozon layer in using or after using flons before giving off into air.
Flons are hydrolyzed and decomposed to form hydrogen chloride, hydrogen fluoride and carbon dioxide gas, and can be collected all as harmless compounds by neutralizing hydrogen chloride and hydrogen fluoride. As the result of our researches to find a catalyst decomposing such flons, we, this inventors, have eventually found that the catalyst comprising alumina or alumina-silica complexed oxide, wherein the alumina containing amount is within a determined range, can decompose flons extremely effectively and can convert into harmless compounds against ozone destruction and have reached this invention.